What Does the Word Littermate Mean?

: one of the offspring in a litter in relation to the others.

Why do puppy littermates fight?

The puppies often become incredibly co-dependent, exhibiting high anxiety when separated. They often fail to bond to their human family as strongly as they otherwise would, if at all. At social maturity, these puppies may begin fighting with one another, often quite severely.

What age does littermate syndrome start?

Littermate Syndrome is the name given to the common behavioral problems that arise when two puppies are raised together beyond the typical 10-12 weeks (about 3 months of age) that professional breeders recommend.